title: Calculation method using Clarkson integration for the physical dose at the center of the spread-out Bragg peak in carbon-ion radiotherapy.
abstract: OBJECTIVE
  In broad-beam carbon-ion radiotherapy performed using the heavy-ion medical accelerator in Chiba, the number of monitor units is determined by measuring the physical dose at the center of the spread-out Bragg peak (SOBP) for the treatment beam. The total measurement time increases as the number of treatment beams increases, which hinders the treatment of an increased number of patients. Hence, Kusano et al. [Jpn. J. Med. Phys. 23(Suppl. 2), 65-68 (2003)] proposed a method to calculate the physical dose at the center of the SOBP for a treatment beam. Based on a recent study, the authors here propose a more accurate calculation method.
  
  
  METHODS
  The authors measured the physical dose at the center of the SOBP while varying the circular field size and range-shifter thickness. The authors obtained the physical dose at the center of the SOBP for an irregularly shaped beam using Clarkson integration based on these measurements.
  
  
  RESULTS
  The difference between the calculated and measured physical doses at the center of the SOBP varied with a change in the central angle of the sector segment. The differences between the calculated and measured physical doses at the center of the SOBP were within ± 1% for all irregularly shaped beams that were used to validate the calculation method.
  
  
  CONCLUSIONS
  The accuracy of the proposed method depends on both the number of angular intervals used for Clarkson integration and the fineness of the basic data used for calculations: sampling numbers for the field size and thickness of the range shifter. If those parameters are properly chosen, the authors can obtain a calculated monitor unit number with high accuracy sufficient for clinical applications.
authors.affiliation: Department of Hospital, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan. m_tajiri@nirs.go.jp
authors.forename: Minoru
authors.initials: M
authors.lastname: Tajiri
authors.forename: Takamasa
authors.initials: T
authors.lastname: Maeda
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Koba
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Isobe
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Kuroiwa
authors.forename: Shigekazu
authors.initials: S
authors.lastname: Fukuda
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Tanimoto
authors.forename: Koichi
authors.initials: K
authors.lastname: Shibayama
mesh_terms: D063193:Heavy Ion Radiotherapy / Q000379:methods*; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012984:Software